I have set up Cakephp with admin login, but I do not have a page design.
Now what?
Do I have the site designed by a web-designer, or will this conflict with the person that is writing my fresh Jquery code.
What about CSS? Is the Jquery developer going to know how to attach them?
What comes first, the horse or carriage? Which ones the horse?
Horse first then carriage.
I would design the HTML/CSS first (or hire it) and then bring in your jQuery jockey.
First build the site to be functional. Then implement js/jQuery to enhance the UI, this is the concept of graceful degradation; the site should work, albeit without the bells and whistles, without any javascript. The javascript just makes it work more easily, more fluidly, more intuitively and more prettily (in theory).
If it's built to standards in the first place, the jQuery guys can come in and make it better. If they have a blank canvas it's too easy to build in logic that can't be replicated without JS.
If you don't even have a page design yet, then discussing things in terms of implementation is decidedly premature.
I'd recommend first that you wireframe your design. Balsamiq is a good option for that, with a 30 day free trial and a reasonable cost (~$80).
Traditionally, that wireframe goes to the designer, who lays things out in photoshop then turns it into HTML/CSS (some skip photoshop). Once it's in HTML/CSS, you have your backend guy go to work, and your frontend guy (who will do the jquery stuff) go to work.
So I guess I'd suggest you get a non-functional design (wireframe or photoshop) pretty well fleshed out before you worry about javascript.
+1 to david thomas too for recommending that you focus on graceful degradation, which would suggest that you should bring in your jquery guy towards the end to add the polish that enhances (but isn't a requirement for functionality).